Automatic telephone system



J 27, 1925. 1,524,194 G. MARTIN AUTOMATIC TELEPHONE SYSTEM F:i 1eg1 July 5, 1920 Inusrz 1:1r

TENS T EMT 4207;? m

Patented Jan. 27, 1925 UNITED STATES PATENT OFFICE.

TALBOT G. MARTIN, OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

Application filed July 3,

To all whom it may concern:

Be it known that I, TALBOT G. MARTIN, a citizen of the United States of America, and a resident of Chicago, Cook County, and State of Illinois, have invented certain new and useful Improvements in Automatic Telephone Systems, of which the following is a specification.

My invention relates in general to automatic telephone systems in which connections are established through the medium of subscriber controlled selector and connector switches, but is more particularly concerned with such automatic telephone systems as include party lines andselective ringing equipment at the central exchange; and the object ofthe invention may be stated to be, broadly, the provision of a new an improved automatic party lineselective ringing system.

Numerous methods of selectively ringing automatic party lines have been devised before this. A system in wide use, which is disclosed in the U. S. patent to Goodrum,

No. 1,156,47 5, involves the provision of differentfrequencies of ringing current at the exchange and tuned bells at the subscribers stations. The connector switches are. divided into groups and each party line is accessible to as many different groups of connectors as there are stations on the line, the connectors of each group being adapted to use a dilferent frequency of ringing cur rent for signalling purposes. Each station on a party line is given a separate telephone number. but all the numbers on a given line are the same except'for the third from the last digit which, as is well known,-is the digit used to control the second selectors in the selection of connector groups. Thus a party line which has, we will say, four stations connected thereto can be reached by four different routes, corresponding to as many different telephone numbers; and

the number selected for use when the line is called will determine the route, or the group of connectors to be used, and therefore the particular station on the line which is to be signalled.

As before stated, systems of the foregoing general description have gone into extended use and have given very satisfactory service. These systems have, however, been used almost exclusively for selective signalling on 1920. Serial No. 393,892.

the so called harmonic principle, in which different frequencies of ringing current are employed in connection with correspondingly tuned bells at the telephones. Now in manual telephone systems a radically different system of selective ringing has been developedfor party line service, depending for its selective action partly on the use of separate ground return signalling circuits, and partly on the use of so called pulsating signalling currents of different polarity. This last described system is in common use by the Bell Telephone Company throughout the United States.

Recently a movement has been started with a view to changing over existing manual plants from manual service to automatic service. In carrying out a change of this kind it is of course necessary to discard the manual switch board entirely and substitute an automatic switchboard: but as to the subscribers telephone instruments it is not generally considered necessary to change these. It is asim-ple operation to install an automatic calling device at each station and the telephones can then be used in connection with an automatic switch board without further change. provided of course that the latter is so designed that it will selectively signal the party line stations in accordance with the system of selective signalling already in use.

In this situation the problem arises of constructing an automatic switchboard or exchange which will successfully signal party lines on which the telephones are constructed and connected according to the above described manual selective ringing principles, and it is this problem that is met and solved by the present invention. The method adopted follows in a general way the four connector group systems of harmonic ringing, already described; but a number of changes and new arrangements have been found to be necessary, and these new improvements together with the operation of the complete system will'be described fully hereinafter reference being had to the accompanying drawing.

In the drawing, which is a circuit diagram of the usual character, I have shown sufiicient of the equipment pertaining to an automatic telephone switchboard wherewlth to establish a connection between a calllng substation A and any one of the four party line-substations A to A inclusive. In view of the fact that much of the apparatus is well known the detailed circuits have in some instances been omitted and the appavselecting switch indicated by the reference character C. The line switch C has access in the usual manner to a plurality of first selector switches and there may 'be second and third selectors also, depending on the capacity of the system. The third selectors have access to the connector switches, and one of these selectors is indicated by the reference character D. The selector D, which is indicated by a simple rectangle, as is the line switch C, is one of a group of similar selectors which have access through their teen multiple'banklevels to ten groups of connector switches. We need to consider, however, only four of these groups, which is the number of. groups required to serve a given group of partly lines, and I have shown in the drawing one connector in each of the four groups. These connectors are indicated by reference characters H to H, inclusive, and connector H is shown complete. Of the remaining connectors all the circuit details are omitted except the ringing circuits.

The four groups of connectors all have access to the same group of party lines. A party line group may consist of one hundred lines which are connected in multiple in the banks of all the connector switches. Thus the party line comprising conductors 111 and 112, which is the line to which substations A to A, inclusive, are connected, is multipled in the bankslof connectorsH to H, inclusive, as shown. It will be noticed that the multiple runs straight through the first two groups of connectors, and through the last two groups, but there is a reversal in 't-he line conductors between theqsecond and third groups.

The party line substations A to A, inclusive, are of well known type and need not be described invdetail. Only the substation A is shown in full, all the circuits of the '-.rest being omitted except the ringing circuits.

T e reference character RM, at the lower left and corner of the drawing, indicates a ringing machine which is assumed to be in continuous operation and which is adapted to impress negative and positive pulsating currents upon the common rin g loads 98 and .99, respectively, at regu ar intervals.

The connections of these ringing leads andthe wiring of the ringing circuits will be described more in detail hereinafter, although it may be stated at this time that the negative lead extends to the connectors in two of the groups while-the positive lead goes to the connectors in the other two groups.

It is thought that the operation of the selective ringing system can best be explained by describing the operations which take place when the several stations on the party linesho'wn in the drawing are called from another station and this will now be done. It will be assumed first that the subscriber at substation A desires to call the subscriber at substation A. When the receiver is removed at substation A the line circuit is closed and the individual line switch C is operated in the usual manner to extend the connection to an idle" first selector switch. Successive operations of the dial now cause the operation of the selected first selector, a second selector and a third selector, the latter of which may be the selector-D, whereby the calling line is entended .to an idle connector in the group of connectors which are adapted to signal the particular substation A.

.Assuming that the connector H is the switch to be used, when the wipers of the selector D connect with the bank contacts in which conductors 13, 14, and 15 are terminated the calling line is extended by way of conductors 13 and 15 to the double wound line relay 17 of the connector H, and this relay is accordingly energized to close acircuit for the slow acting release relay 18. The latter relay, upon energizing, prepares the connector for operation in its vertical movement and also, at its upper armature, grounds the release trunk conductor 14, thereby establishing a holding circuit for the preceding switches which are in use in the connection.

I The circuit. interruptions caused by the next operation of the calling dial cause the line relay 17 to be deenergized a plurality of times and this relay at each deenergization transmits an impulse of current to the vertical magnet 25. The circuit includes the off normal springs27 and 29 and the winding of the slow actin relay 19, and may be traced without di culty. By the operation of the vertical magnet the shaft is raised step by step until the wipers 50-52, inclusive, stand opposite the desired level of bank contacts. At the first upward movement of the shaft the off normal springs are shifted and spring 27 is disengaged from spring 29 and is brought into engagement with spring 28, but since the slow acting relay 19 is now energized the 19 falls back and transters the operating circuit to the rotary magnet 24.

\Vhen the calling dial is operated in accordance with the next and final digitthe line relay 17 sends a series of impulses to the rotary magnet 21 and this magnet is operated to rotate the shaft step by step until the wipers 5(l52, inclusive, are finally brought to rest in engagement with bank conta ts 5355. inclusive. During the rotation of the switch the slow acting relay 22 is energized in parallel with the rotary magnet and maintains its armature continuously attracted. In energized position relay connects the test wiper 51 to the test relay 21, so that if the called line is busy the ground potential on the contact, 54 will cause the said test relay to be energized. lelay 21. prepares a locking circuit for itself at its upper armature which is losed when relay 22 deenergizes at the end of the. rotary movement, and at itslower armature connects the busy lead 30 to the lower heavy talking conductor, thusgiving the calling subscriber a busy signal. o may assume. however. that the line is idle when called. and under these circumstances when the connector completes the connection as des'ribed in the foregoing the test wiper 51 will find no ground potential and the test relay 21 will not be energized. Then when the slow acting relay 22 falls back at the end of the rotary movement. a circuit is completed from the grounded conductor 14 by way of the upper winding of the switching slay 23, the test wiper 51. test contact 54, and the winding of relay 109 to battery. Relay 109 is the cut-off or switching relay ot' the individual line switch C allotted to the called line and is energized to disconnect the line from its normal battery and ground connections (not shown) in the line switch. The switching relay 23 in the connector is also energized and grounds the test. wiper 51. closes a locking circuit torits lower winding. opens the rotary magnet circuit. and finally, at its two outside armatures, connects up the line wipers and 52.

The connection to the called line has now been completed and the ringer at substation A. which, it may be stated. is adapted to respond to negative pulsating current, is operated in the following Tnanner: A circuit for the alternating current relays 1.13 and 133 at substations A and A may be traced from the ringing machine RM by way oi negative ringing lead 98.,the upper winding of ring cut-off relay 20. the upper talking conductor of the connector. line wiper 50 and bank contact 53 engaged thereby. andline conductor 112 to substation A where the circuit divides, one branch extending by way of condenser 11.5, resistance 114. and A. C, relay 113 to ground and the other branch continuing to substation A where it extends by way of condenser 13.3. resistance 134, and A. C. relay 133 to ground. Due to the condensers in the parallel branch circuits to ground at the two substations, alternating currents are set up in the two A. C. relays 113 and 133 and these relays are operated to connect ringers 117 and 137 in bridge of the line. As soon as these ringers are connected across the line part of the current will flow through the two ringers in parallel to line conductor 111. and thence by Way of said line conductor, bank contact 55 and wiper 52to ground at the lower armature of the ring cut ofl relay 20. Ringer 117 is adapted to respond to negative pulsating current, as stated, while ringer 137 is adapted to respond to positive pulsating current, and it follows therefore that since the current is being supplied from the negative ringing lead 98 only the ringer 117 will be operated. It is understood of course that in the normal operation of the ringing machine the lead 98 is disconnected at intervals and it is connected to the negative pole of battery, thus causing the ringer 117 to be actuated intermittently in the well known manner.

The subscriber at sub-station A is now being signalled and his bell will continue to ring until he answers or until the calling subscriber hangs up his receiver. In this connection it should be mentioned that the cut off relay 20 is so adjusted that. it will not respond or be operated under ringing conditions. The resistances in circuit at the substations limit the current flow, and relay 2O moreover is provided with a copper slug which greatly reduces the effect of the alternating component ot the current. The relay therefore may be readily adjusted so that it will not operate during ringing. \Vhen the subscriber at substation A answers, however, a low resistance bridge is closed across the line through the transmitter and the primary winding of the induction coil and cut off relay 20 is instantly operated. either by current from the battery normally included in the ringing circuit (at any time when this battery is not oplit) posed by the A. C. generator) or by curv rent from the battery to which the lead 98 is connected during the silent periods. Upon energizing. relay 2O establishes a locking circuit for itself at its inner armature and at its two outside armatures breaks the ringing circuit and finally completes the talking circuit.

As soon as the talking connection is closed by the ring cut oil relay 20. the back bridge relay 16 is energized by current supplied to the called line for talking purposes and reverses the direction of current flow in the calling line in the usual manner. This is the customary means. provided for operating a meter orcoin collect device and being a standard arrangement the circuits are shown this way although -no meter or other mechanism is shown. Conversation may now proceed as. desired and when the subscribers are through they will both replace their receivers. By the replacement of the receiver at substation A the entire connection is released in the usual manner. When the line circuit is opened the line and rein signaling the subscriber at substation A,

I will now explain briefly how the subscribers at the other substations on the same line are signalled. It was described fully in the course of the preceding explanation how ringers 117 and '137 areconnected across the line by the operation of A. C. relays 113 and'l33, located at substations A and A, respectively, and actuated by the application of ringing current to line conductor 112. In the case described ringer 117 was actuated because. negative pulsating current was used. It will be seen now that if a connector in the second group, connector H for example, is used to set up the connection positive pulsating current from the positive ringing lead 99 will be applied to-the called line instead of negative pulsating current. With this exception all the conditions are the same and it follows that the ringer 137 at substation A will be operated, for this ringer, as before stated, is adapted to respond to positive pulsating current. The routing of the call by way of a connector in the second group is of course determined by the third from the last digit in the telephone number, and except as to the connector used the connection is established in the same way as in the preceding case. M

At substations A and'A the A. C. relays are connected from conductor 111 to ground. In order to apply ringing current to this conductor at the exchange the line conductors are reversed in the banks of the two remaining groups-,of connectors, as shown in the drawing, so that the upper wiper of any connector in these two groups which is'operated-will connect with conduc- 9s tor 111 rather than with conductor 112.

Since the negative ringing lead supplies ringing current to the connectors of the third group and the positive ringing-lead to those in the fourth grou and since the ringers at substations A an A are ada ted to respond to negative and positive pu sating currents, respectively, the operation of selectively signalling these last two stations will now be readily understood. Substation A is called .by way of a connector in the third group, connector H for exam le, and substation A is called by way of a connector in the fourth group, such as connector H. v

Before. closing, particular attention is called to the fact that the circuits and wiring of the connector switches is absolutely uniform throughout the four standing the fact that the ringing operation performed is different in each group. To be more specific, it is pointed out that ringing current is applied to the called line by way of the upper wiper in all, the connectors, and the ring out off relays in all the connectors are wired exactly alike. This is an extremely desirable feature because in the course of the operation of an exchange the switches are removed from time to time for adjustment and on this account are preferably made interchangeable. The cost of manufacture is also reduced by having the connectors all uniform. To provide for using the upper wiper for ringing in all the connectors, a simple reversal in the lines between the second and third connector groups is all that is necessary. This has been pointed out before. To secure uniform wiring of the ring cut oil relays, however, is some what more diflicult. It will be understood of course that the two windings of one of these relays must be soconnected that the current flow in the locking winding will assist rather than op the current in the upper winding when t e relay is operated by the removal of the receiver on a called line. Since negative pulsating current is used by the connectors in two of the groups and positive by the connectors in the other two groups it will be evident that if the locking windings of all the relays are connected the same the upper windings must be reversed in the case of the relays in two of the groups. This reversal is not done in the connectors, however, but outside. known the incoming trunk conductors and the various power wires, etc., are in practice wired to so called female jacks on the shelf on which the connectors are mounted, and the, relays andmagnets of the switch are wired to corresponding male jacks which are mounted on the switch frame. When the switch is in position the male and female jacks engage and the various circuits are thus connected up. I provide for each 0onnector Switch three extra pairs of jack:

groups, notwith- As is well which in the case of the connector H are indicated by reference characters 72, 73, and

74:, The small circles represent the female jacks mounted on the switch shelf and the arrow heads indicate the male jacks which are mounted on the frame of the switch. The ring out oflf relay is permanently wired to the three male jacks associated therewith in the manner shown and an inspection of the drawing will show that the ring cut oii relays and 90 are wired in exactly the same manner. This is true also of the ring out ofl relay 20 of the connector H in the first group, although the details are not shown. The positive ringing lead 99 supplies ringing current to all connectors in the second and fourth groups and is connected in multiple to the middle female jacks of the extra pairs, as shown in the drawing in the case of connectors H and H. The negative ringing lead is similarly multipled through the first and third connector groups, but is connected to the lower female jack of each extra set, as shown in the case of con- 1'1ecto;'-H The two vacant female jacks of each set are then strapped together as shown. With the above described arrangement although the connectors are allabsolutely alike nevertheless the upper windings of the ring out off relays in two of the groups are reversed when the connectors are mounted on the shelves, and notwithstanding the use of ringing currents of opposite polarities the upper and lower windings of all the ring out off relays are properly connected so as to coo erate with each other. I

f aving described my invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out more specifically in the appended claims.

What I claim is:

1. In an automatic telephone system, party lines, sources of positive and negative pulsating current at the exchange, a plurality of groups of connector switches for calling one of said lines and for connecting said sources thereto for selectively signaling the stations thereon, all of said connectors being alike and interchangeable between groups, and a ring out off relay in each of said switches having a locking winding independent of the signalling circuit.

2. In an automatic telephone system, a four party line, biased ringers at the stations on said line, sources of positive and negative pulsating current at the exchange, four groups of connector switches for calling said line and for connectin the said current sources thereto for selectively signalling said stations, all of said connectors being alike and interchangeable between groups and a ring cut-oil relay in each connector having a winding included in the signalling circuit and a holding winding independent of the signalling circuit.

3. In an automatic telephone system, a four party line, biased ringers at the stations on said line, sources of positive and negative pulsating current at the exchange, four groups of connector switches for calling said line and for connecting the said current sources thereto for selectively signalling said stations, a ring cut-off relay in each connector having a winding included in the signalling circuit when the connector is in use for signalling and a locking winding energized while the connector is in use for talking, and circuit connections outside the said connectors permitting the said ring cut off relays to be all wired and connected in an identical manner, whereby the said connectors are made interchangeable between the said groups.

4. In an automatic telephone system, a four party line, biased ringers at the stations on said line, sources of positive and negative pulsating current at the exchange, four groups of connector switches for calling said line and for connecting the said current sources thereto for selectively signalling said stat-ions. ring cut-off relays in said connectors each having a winding adapted for inclusion in an established signalling circuit and a locking winding, all the said relays being wired and connected within the connectors in an identical manner, and circuit connections outside the said connectors such that both windings of each of said relays cooperate when the said relays are energized.

5. In an automatic telephone system, a party line, sources of positive and negative pulsating current at the exchange, groups of connector switches for calling said line and for connecting the said current sources thereto for selectively signalling said stations, ring cut-oif relays in said connectors each having av pull up winding adapted for inclusion in an established signalling circuit and a. locking winding, three special terminals on each connector, an outgoing ringing conductor and conductors from the pull up winding of the ring cut-off relay in each connector, the said conductors being connected to the associated special terminals in identically the same way in each connector, other terminals for each connector engaged b said first named terminals when the swltches are mounted on the switchhoard, and circuit connections at the said other terminals associated with each connector includin an incoming ringing conductor connected to one of them such that both windings of each ring cutoff relay will coope ate when the said relays are energized.

6. In an automatic telephone system, a party line, biased ringers at the stations on said line, sources of positive and negative pulsating current at the exchange, groups of connector switches for calling said line and for connecting the said current sources thereto for selectively said stations, side the said connectors such that both windring cut-off relays in said connectors each, ings of each of said relays co-operate when having a winding ada ted for inclusion in the said relays are energized.

an established signalling circuit and a lock- Signed by me at Chica 0, Cook County, 5 ing winding, all the said relays being wired Illinois, this 28th day of une, 1920.

and connected within the connectors in an H identical maner, and circuit connections out- TALBOT G. MARTIN. 

